Implement from_scratch option

Fixes #934, and also helps with #1173.

beets/config_default.yaml

@@ -10,6 +10,7 @@ import:
     delete: no
     resume: ask
     incremental: no
+    from_scratch: no
     quiet_fallback: skip
     none_rec_action: ask
     timid: no

beets/importer.py

@@ -534,6 +534,10 @@ class ImportTask(BaseImportTask):
     def apply_metadata(self):
         """Copy metadata from match info to the items.
         """
+        if config['import']['from_scratch']:
+            for item in self.match.mapping:
+                item.clear()
+
         autotag.apply_metadata(self.match.info, self.match.mapping)
 
     def duplicate_items(self, lib):

beets/library.py

@@ -561,6 +561,11 @@ class Item(LibModel):
         if self.mtime == 0 and 'mtime' in values:
             self.mtime = values['mtime']
 
+    def clear(self):
+        """Set all key/value pairs to None."""
+        for key in self._media_fields:
+            setattr(self, key, None)
+
     def get_album(self):
         """Get the Album object that this item belongs to, if any, or
         None if the item is a singleton or is not associated with a

beets/ui/commands.py

@@ -1004,6 +1004,10 @@ import_cmd.parser.add_option(
     u'-I', u'--noincremental', dest='incremental', action='store_false',
     help=u'do not skip already-imported directories'
 )
+import_cmd.parser.add_option(
+    u'--from-scratch', dest='from_scratch', action='store_true',
+    help=u'erase existing metadata before applying new metadata'
+)
 import_cmd.parser.add_option(
     u'--flat', dest='flat', action='store_true',
     help=u'import an entire tree as a single album'

docs/reference/cli.rst

@@ -111,6 +111,12 @@ Optional command flags:
   time, when no subdirectories will be skipped. So consider enabling the
   ``incremental`` configuration option.
 
+* When beets applies metadata to your music, it will retain the value of any
+  existing tags that weren't overwritten, and import them into the database. You
+  may prefer to only use existing metadata for finding matches, and to erase it
+  completely when new metadata is applied. You can enforce this behavior with
+  the ``--from-scratch`` option, or the ``from_scratch`` configuration option.
+
 * By default, beets will proceed without asking if it finds a very close
   metadata match. To disable this and have the importer ask you every time,
   use the ``-t`` (for *timid*) option.

docs/reference/config.rst

@@ -475,6 +475,15 @@ Either ``yes`` or ``no``, controlling whether imported directories are
 recorded and whether these recorded directories are skipped.  This
 corresponds to the ``-i`` flag to ``beet import``.
 
+.. _from_scratch:
+
+from_scratch
+~~~~~~~~~~~~
+
+Either ``yes`` or ``no`` (default), controlling whether existing metadata is
+discarded when a match is applied. This corresponds to the ``-from_scratch``
+flag to ``beet import``.
+
 quiet_fallback
 ~~~~~~~~~~~~~~
 

test/test_importer.py

@@ -633,6 +633,17 @@ class ImportTest(_common.TestCase, ImportHelper):
         self.assert_file_in_lib(
             b'Applied Artist', b'Applied Album', b'Applied Title 1.mp3')
 
+    def test_apply_from_scratch_removes_other_metadata(self):
+        config['import']['from_scratch'] = True
+
+        for mediafile in self.import_media:
+            mediafile.genre = u'Tag Genre'
+            mediafile.save()
+
+        self.importer.add_choice(importer.action.APPLY)
+        self.importer.run()
+        self.assertEqual(self.lib.items().get().genre, u'')
+
     def test_apply_with_move_deletes_import(self):
         config['import']['move'] = True